Textile fibers and their manufacture



1 AK m i s\ June 12, 1962 J. ZIMMERMAN 3,033,235

TEXTILE FIBERS AND THEIR MANUFACTURE Filed Dec. 6. 1956 '2 Sheets-$heet l 1 12;. I j [fl 3.1a

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. INVENTOR JQSEPH ZIMMERMAN ATTORNEY June 12, 1962 J. ZIMMERMAN TEXTILE FIBERS AND THEIR MANUFACTURE 2 Shets-Sheet 2 Filed Dec. 6, 1956 Ei'g. 7

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INVENTOR JOSEPH ZIMMERMAN ATTORNEY United States Patent 3,038,235 Patented June 12, 1962 Free 3,033,235 TEXTILE FIBERS AND THEIR MANUFACTURE Joseph Zimmerman, Wilmington, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Deb, a corporation of Delaware Filed Dec. 6, 1956, Ser. No. 626,675 15 Claims. (Cl. zit-82) This invention relates to textile fibers and particularly to textile fibers possessing a permanent crimp.

It has been proposed to spin different fiber-forming materials together in such a fashion that the materials form a unitary filament which contains the components in an eccentric relationship across the filament. After stretching these composite filaments and then relaxing or shrinking them, a difierence in contraction between the two components in a filament will produce a spirally crimped filament in which the component having the greater shrinkage will be situated on the inner side of the helical coil. These crimped filaments, however, upon the application of only moderately high tension, do not exhibit high crimp retention. This tendency to lose crimp after being subjected to tension is a serious limitation on the utility of such filaments in the textile industry.

C-opending applications of Alvin L. Breen, filed February 26, 1954, Serial No. 412,781, now US. Patent 2,931,091, and Serial No. 412,871, now abandoned describe new and improved crimped filaments having a greatly improved crimp retentivity under tension, as for example when fabricated into knitted articles, and, in addition, possess a higher degree of crimp (e.g., 40 to 80 crimps per inch) than the filaments of the prior art; these properties, among other things, adapt these new yarns to use as elastic fibers. In crimped form, these new fibers assume a helical or coiled form like the appearance of a coiled spring, the helices reversing their direction at irregular intervals, usually about every one-quarter to one-half inch, depending upon the d.p.f. (denier per filament) and upon the coil diameter.

These self-crimped yarns, however, are unstable towards heat. For example, such yarns, in their uncrimped but potentially crimpable state, may be fabricated into articles and then have their crimp developed by immersion in water at 70 to 100 C.; if, however, they are thereafter subjected to higher temperatures, a loss in crimp may result. Thus, in the manufacture of elastic half hose composed of yarn, a sock can be knitted of a potentially self-crimpable yarn, then placed on a forming board and crimped in situ by exposure to hot water or steam; if the sock is then subjected to a dye bath under a higher temperature, e.g., in dyeing under pressure, some loss in crimp takes place, together with some wrinkling; the socks are then freed from wrinkles by placing on another form and dried in air at temperatures about 160 C. which is con-' siderably higher than the temperatures of the previous treatments; exposure to this latter step may result in further loss of yarn crimp and hence a loss in the elasticity of the sock.

It has been discovered, in accordance with the present invention, that composite crimped filaments having greatly improved properties, particularly with respect to retention of crimp after heat treatment, can be obtained by spinning as one component a polymer having a molecular weight substantially below that acceptable for the commercial spinning of fibers, said component having a low degree of shrinkage in the composite filament to be crimped, the other component, which is the load bearing component, being a polymer having a molecular weight admirably suited for the commercial spinning of fibers and having a substantially higher degree of shrinkage than said low molecular weight component in the potentially crimpable composite filament. The value of this discovery applies not only to the production of crimped filaments but also to the production of potentially self-crimpable filaments from which the crimped filaments are derived at any desired time by suitable relaxation to develop crimp.

It is, therefore, an object of the present invention to provide new potentially self-crimpable filaments and new crimped filaments having greatly improved properties and utility. It is a further object of the invention to provide composite crimped filaments having improved crimp retentivity. Another object of the invention is to provide highly crimped synthetic linear polymer yarn having high resistance to loss of crimp upon being subjected to high temperature. Other objects will appear hereinafter.

The objects of this invention have been accomplished, in general, by spinning a composite filament in which the lower shrinking component has a molecular Weight of or less of the molecular weight acceptable as a minimum for the commercial production of fibers. One way of measuring molecular weight is by relative viscosity of the polymer which, for the low shrinkage component should be 20 or less, this viscosity insuring a sutficiently low degree of shrinkage for the low shrinkage polymer. Where relative viscosity for a particular polymer has not been determined, other methods for determining molecular weight, e.g., by intrinsic or inherent viscosity measurement, may be used; thus, even in this case, the molecular weight in question corresponds to that within the range of determinable relative viscosities. The higher shrinkage component, which is the component bearing the load placed on the crimped filament and .is hence termed the load-bearing component, will have a molecularweight suificiently high for commercial production of fibers and will inherently have a substantially higher degree of shrinkage than the lower molecular weight polymer in the filament which is to be given the crimping treatment; generally speaking, the relative viscosity of the higher shrinking or load-bearing component will be at least 22 and ordinarily at least 27.

The term fiber forming as used herein with respect to polymers and filament components, signifies acceptability for forming fibers according to the standards required for the commercial production of filaments.

Referring to the drawings:

FIGURE 1 is an elevation in section along a longitudinal central plane of a spinneret assembly which can be used to make the composite filaments of this invention;

FIGURE 1A is an enlarged section of a portion of FIGURE 1;

FIGURE 2 is a transverse cross-section of the apparatus of FIGURE 1 taken at 22 thereof and showing a plan of the front or bottom spinneret plate;

FIGURE 3 is a transverse cross-section taken at 3-3 of FIGURE 1 to show the plan of the top of that plate thereof;

FIGURE 4 is a transverse cross-section taken at 4-4 of FIGURE 1 to show the plan of the bottom of the top plate thereof. FIGURES 5, 6 and 7 show magnified cross-sections of filaments of the present invention.

It is preferred that the present invention be applied to the production of sheath-core filaments having a core which is kidney-shaped in cross-section, such kidneyshaped cores being described and defined in the copending application of Alvin L. Breen Serial No. 614,640 filed October 8, 1956, now US. Patent 2,987,797 which also shows a specially designed spinneret for producing such filaments. The invention will, therefore, be described particularly with reference to the apparatus of said Breen U8. Patent 2,987,797, which is illustrated in FIGURES 1, 1A, 2, 3, and 4 of the present drawings.

It will be understood, however, that any other suitable equipment may be used, for example, those described in the copending applications of Alvin L. Breen, filed February 26, 1954, Serial No. 412,781, now US. Patent 2,931,091, and Serial No. 412,871, now abandoned, which disclose spinnerets for the production of side-by-side twocomponent filaments and sheath-core filaments in which the core is eccentric with rmpect to the sheath.

In all the figures, 1 represents the front or bottom plate provided with extrusion orifices 2 and recessed at the back to form plateau-like protrusions 4. Each extrusion orifice 2 consists of an extrusion capillary 21 at the exit end and a larger counterbored portion 22 connecting the capillary with the top of the protrusions 4. Back or top plate 7 is sealed against and spaced from the front plate by gasket 6 and shim 16, the former being ring-shaped and located near the periphery of the opposing faces of the two plates, and the latter being disc-shaped and located concentric with the two plates. Relatively unrestricted region 12 between the two plates is interrupted at intervals by constricted regions 15 between the opposing face of the back plate 7 and plateau face of the protrusions 4 from the front plate. The back plate is partitioned on top by outer wall 19 and inner wall 29 into annular chamber 8 and central chamber 9. The annular chamber communicates with the constricted regions 15 between the two plates through counterbored core feed apertures 10, consisting of terminal capillary 23 and counterbore 24, and the central chamber 9 communicates with the intervening relatively unrestricted region 12 through sheath feed apertures 11. The two plates are retained in place by screw cap 18 threaded onto the end of the back plate. The upper part of the housing (not shown) receives suitable piping or other supply means for separately supplying core and sheath forming material to the two chambers 8 and 9, which may be provided with distribution or filtering spaces as desired. Pin 14 through cylindrical openings 25 and 26, in the front and back plates respectively, near one edge of the plates ensures the desired alignment of the two plates.

The back plate 7 is provided with a tapered circular groove 3 shown more clearly in FIGURES 1A and 4 which is positioned so that its shallowest depth is tangentially contiguous to each of the terminal capillaries 23. The size and shape of this groove influences the shape of the sheath and cores of the filament being extruded.

FIGURE 2 is a transverse plan section of the front plate. Appearing in this view are eight plateau-like protrusions 4, each with a plateau face 5, each concentric with an extrusion orifice 2 and uniformly spaced about a circle inside the outer gasket 6.

FIGURE 3 shows the appearance of the back plate sectioned as indicated in FIGURE 1, showing the concentric outer and inner walls 19 and 29, the capillaries 23 and counterbores 24 of eight core-feed apertures spaced uniformly on a circle between the two walls 19 and 29, and four sheath-feed apertures 11 located within the central chamber 9 defined by the inner wall 29.

Operation of the described apparatus in the practice of this invention is readily understood. Separate polymers are supplied to the central and the outer cylindrical chambers 9 and 8, respectively, of the back plate; the former fiows through the openings 11 into the relatively unrestricted region 12 between back and front plates, through the relatively constricted regions between the plateau face 5 and the opposing back plate face, and through the extrusion orifices 2 and capillary 21 to form the sheath of a filament while the latter passes first through the core-feed apertures 10 in the back plate 7 and directly into and through the aligned extrusion orifices 2 and extrusion capillary 21 in the front plate to form the core of the component.

The apparatus as depicted in FIGURES 1, 1A, 2, 3 and 4 but without groove 3 will afford a sheath-core yarn with concentric arrangements of the sheath and core if the orifices of the two fiber-forming components are coaxial or nearly so and the protrusions 4 are concentric about each extrusion orifice 2 and extrusion capillary 21 in the spinneret plate, and the plateau face 5 is parallel to the lower face of the back plate 7. To obtain the composite filament with a kidney-shaped core, as shown in FIGURE 7, the spinneret assembly is made, as shown more clearly in FIGURES 1A and 4, by the inclusion of a groove 3 cut as a ring around the terminal capillaries 23 in the top plate. This grooved ring provides an unsymmetrical flow resistance over the plateau so that a filament with a core kidney-shaped in cross-section is produced similar to FIGURE 7.

The expression relative viscosity (nr) as used herein, signifies the ratio of the flow time in a viscosimeter of a polymer solution containing 8.2% 510.2% by weight of polymer in a solvent, relative to the flow time of the solvent by itself. Measurements of relative viscosities given in the examples were made with the following solutions: 5.5 g. of a polyamide in 50 ml. of formic acid at 25 C. or 2.15 g. of the polyester in 20 ml. of a 7/10 mixture of trichlorophenol/ phenol at 25 C.

The expression inherent viscosity as used in the examples is defined as:

lnnr

wherein c is the concentration in grams of the polymer in ml. of the solvent and 'qr is the symbol for relative viscosity and In is the logarithm to the base e. The viscosity measurements for calculating the inherent viscosity are made on /2% solutions by weight at 25 C. Meta-cresol and a 7/ 10 mixture of trichlorophenol/phenol are used as the solvents for polyamides and polyesters respectively in this determination.

The expression intrinsic viscosity as used herein signifies the extrapolated value of inherent viscosity lmyr at the ordinate axis intercept (i.e. when 0:0) of an extended line of inherent viscosity values in a graph of lmyr as ordinates with 0 values as abscissae; ln, nr and c are as above in the formula for inherent viscosity.

Number average molecular weights, designated herein by the symbol m, have been obtained by known end group or osmotic pressure determination.

The potential elastic extensibility of the crimped yarns which is due to the tightness of the spiral crimp developed has been termed percent crimp elongation and is calculated as follows:

Lr t X100 where L is the length of the yarn under such tension as is required to straighten all the crimps and L is the length of the crimped yarn after the tension is released. For a given filament and helical diameter, the percent crimp elongation is proportional to the number of crimps per inch.

Another parameter or variable that is of interest in helically crimped yarns is the crimp or coil modulus that determines how readily the crimp is pulled out, i.e., the snap of the crimped yarn. By analogy to a spring, the crimp modulus is directly proportional to the shear modulus of the load-bearing polymer and to the square of the filament diameter. The latter is directly proportional to the filament denier for polymers of similar density. The crimp modulus is inversely proportional to Percent crimp elongation:

the square of the mean diameter of the spring or filament helix. The crimp modulus is also inversely related to the number of coils per unit length. Although it is very difiicult to measure crimp modulus directly, relative values can be estimated by separately determining the above 5 variables in diiferent crimped yarns.

The stability of the crimp in the filament to mechanical deformation has been measured in the past by the crimp retentivity test of Hardy and Miles U.S. Patent No. 2,387,- 099. This test measures the amount of crimp regained by yarn which was relaxed under no tension after having been submitted to a tension of 0.03 grams per denier for 30 seconds in 60 C. water. The crimped yarns of the .prior art had crimp retentivities of from 60% to 100%. This test was of little value in evaluating the filaments of this invention since, although crimp retentivities of 85% to 100% were commonly observed for the yarns of this invention, some prior art yarns exhibited crimp retentivities within this range. Accordingly, higher tensions were employed in this test. Even after an applied tension of 1 gram per denier for 15 seconds in air at room temperature, 97% of the crimp was regained after relaxation in the crimped filaments of this invention. 95100% of the crimp was regained in the crimped filaments of this invention which were relaxed after a tension of 0.1 gram per denier was maintained on the crimped yarn for 24 hours at room temperature.

Whereas crimped filaments of the prior art exhibited as little as 60% crimp recovery from a 10% stretch and a -second exposure to boiling water in the stretched 30 condition after a one minute relaxation free of tension in air, the filaments of this invention all showed 80% to 90% crimp recovery under the same conditions, and 90% to 100% crimp recovery after a two minute tension-free relaxation in boiling water instead of in air.

The following examples in which parts, proportions and percentages are by weight unless otherwise indicated are intended to illustrate rather than to limit the invention.

EXAMPLE I (a) Molten poly(ethylene terephthalate) made as described by Whinfield and Dickson in U.S. Patent No. 2,465,319, with a relative viscosity of 16.4 and an intrinsic viscosity of about 0.43 (m estimated at about 9,000) was melt-spun as cores of two component fibers using an assembly similar to that depicted in FIGURES 1, 1A, 2, 3 and 4 except that the spinneret had 34 holes. Poly(hexamethylene adipami'de) of relative viscosity 41 (MT, of 15,000 and an inherent viscosity of 1.03) was 5 simultaneously melt-spun as sheaths of the composite filaments. The pump speeds were adjusted to give a sheath/ core ratio by volume of /45, the two polymers were co-spun at 290 C. into air at 25 C., and the resulting yarn wound up at 800 y.p.m. (yards per minute). The 55 yarn had the cross-section shown in FIGURE 7. The yarn was drawn 266% over a hot draw pin at 83 C plate at 140 C., and wound up at 153 y.p.m. Skeins of the yarn respectively under tensions of zero and 0.00065 g.p.d. (grams per denier), the latter of which corresponds approximately to the restraining force inherent in knitwear, were then placed in C. Water which caused the development of a spiral-type crimp in the yarn. The effect of heat on the crimp was determined by placing a measured length of crimped yarn, with its known percent crimp elongation, free of tension, into a dry oven at 180 C. for a given period (10 minutes), and measuring the percent crimp elongation after the heating. The difference between the percent crimp elongation before and after heating is percent crimp elongation loss. The same percentage loss of crimp was obtained regardless of the tension under which the yarns were crirnped, i.e., zero vs. 0.00065 g.p.d.

(b) The low viscosity poly(ethylene terephthalate) used in the above Example 1(a) was replaced with poly- (ethylene terephthalate) of relative viscosity 33 (intrinsic viscosity of about 0.66 and an estimated m of about 18,000) and a composite filament spun under the same conditions as in Example 1(a). The cross-section of the filaments were similar to those of FIGURE 7 but approaching slightly more to the elliptical than in FIGURE 7. The yarn was drawn, stabilized by passing over and in contact with a hot plate and crimped in the same way as in Example 1(a).

(c) In a third spin, the above procedure of Example I( b) was repeated but the positions of the polyester and the polyamide were reversed so that each composite filament formed had a polyamide core enclosed by a high viscosity polyester sheath.

Monofilaments spun from the polyamide used in the above examples had a boil-ofi shrinkage (when shrunk free of tension) of 10.5% after a 300% draw over a draw pin maintained at 85 C.; the same monofilaments had a boil-off shrinkage of 8.3% after a 300% draw over a draw pin maintained at 83 C. followed by stabilization of the filament length by passage over and in contact with a hot plate maintained at C. A monofilament of the second-named polyester (33 relative viscosity) had shrinkages of 11.5% and 4.5%, respectively, when tested under the same conditions. Although a monofilament of the first-named polyester (16.4 relative viscosity) could not be spun, this polyester exhibited less shrinkage than the polyamide of this example as evidenced by its location on the outside of the helix of the composite filament.

Thus, in this hot pin, hot plate drawn composite filament, the polyester is the lower shrinking component of the filament and the polyamide becomes the load-bearing component of the filament regardless of the relative position of the polymers in the filament.

The amount of crimp developed as measured by the percent crimp elongation, its loss on heating, the number of complete helices per inch in the crimped yarn, the radius of curvature of the helices and other data are given in Table I which follows:

Table I Polymer Yarn Relative viscos- Denier Percent crimp Percent Reference Type ity (drawn) Com- Radius elongation from crimp yarn plete l of curvacrimping tension elongadenger-f tumg/ tureh tion loss num er 0 me in inc es 10 min Sheath Gore Sheath Core filaments 0 .00065 180 C g.p.d.

Example I(a) Polyamidm. Polyester 41 16. 4 149-34 60 019 287 200 60 Example 1(1)) do d0 41 33 -34 64 019 300 95 Example 1(0)"... Polyester Polyam1de 33 41 134-34 59 020 270 134 90 1 Measured on yarn crimped under no tension.

the polyester core stabilized against shrinkage by passage of the composite filaments over and in contact with a hot The data indicate that by use of a low viscosity polyester core, greater heat stability of the crimp is obtained than in a filament of similar construction using a high viscosity polyester core. These characterization tests on yarn were further confirmed by comparable data obtained by knitting tubing and socks of the above yarns after the drawing and stabilization step but before crimping, exposing the fabricated articles with wet steam at 100 C. to crimping conditions on a boarding form, then dyeing at 110 C., and drying on a form at 120 C. to 130 C.

When the low molecular weight polyester core (relative viscosity 16.4) was replaced with an 85:15 mixture by weight of poly(ethylene terephthalate) having a relative viscosity of 19 and poly(hexamethylene adipamide) of relative viscosity 10 while using the same sheath material of Example 1(a) above, good crimped yarns were obtained upon relaxing the drawn and hot plate treated yarns in 60 C. water. The yarn was inferior to the above-mentioned crimped yarns using only low viscosity polyester, in crimp elongation, but showed improved resistance to filament splitting due to improvement in the adhesion between the sheath and core components.

When the core material of the last paragraph is replaced with an 85: blend of the polyester and the polyamide, but of higher composite molecular weight while using the same sheath material, a crimped yarn of inferior crimp elongation and inferior thermal crimp stability is obtained.

EXAMPLE II Using the equipment and technique of Example I, yarn of composite filaments was made of poly( ethylene terephthalate) of relative viscosity 17 m of about 9000, and an inherent viscosity of about 0.44) as a core and poly (hexamethylene adiparnide) of relative viscosity 50 m of 17,500 and an inherent viscosity of 1.12) as a sheath. The resultant crimped yarns when exposed free of tension to 180 C. dry heat for ten minutes lost only 30% to 35% of their crimp as compared to a 60% loss with the best item in Example I. The data for this example is given (b) The process of Example III (a) was repeated using poly(hexamethylene adipamide/terephthalamide) 70/30 by weight of relative viscosity 1 1 and an inherent viscosity of about 0.59 as a sheath and poly(hex-amethylene adipamide/epsilon caproamidc) 60/40 by weight of relative viscosity as the core. Despite the low molecular weight of the first copolymer, it could be satisfactorily spun as a sheath due to its abnormally high melt viscosity, two to three times that for polyhexarnethylene adipamide of the same molecular weight. A monofilamerit of this polymer shrunk 5% in boiling water under 0 g.p.d. tension after spinning and drawing as above.

Both composite yarns developed an excellent crimp of 250% to 280% crimp elongation in 95 C, water. '[he crimped yarn of Example 111 (b) containing the low molecular weight polymer lost only about 5% of its crimp after ten minutes at 180 C. while the other yarn of Example 111 (a) lost 65% of its crimp under the same conditions.

EXAMPLE IV Various low molecular weight polymers containing an aromatic group intralinear to the polymer chain were prepared by known methods and spun as the core of composite filaments surrounded by a sheath of poly(hexamethylene adipamide) of relative viscosity 41. A yarn with a core of poly(hexamethylene adipamide) of relative viscosity 10 but with the same sheath material was spun as a control. The cross-sections of all filaments were similar to those of FIGURE 7. All yarns were drawn about 300% over a pin at 80 C. followed by passage over and in contact with a plate at 160 C. Skeins of all the yarns developed a good spiral crimp on two minutes immersion in 95 C. water. The results are shown in Table III. The low molecular weight aromatic core polymers all shrank less than the sheath polymer as evidenced by their being located on the outside of the helix of the crimped filament.

All yarns of this Example IV showed the superior in Table II which follows. 40 thermal crimp stability (10-40% crimp loss) that has Table II Polymer Yarn Type Relative viscos- Denier Percent ity (drawn) Com- Radius Percent crimp yarn plete 1 of curvacrimp elongadenier turns] ture 1 elonga tion loss Sheath Core Sheath Core number of inch in inches tion 1 10 min./

filaments 180 C.

Polyamide (Ex. 11)-..- Polyester 17 85-34 83 .015 315 30-35 1 Measured on yarn crirnped under no tension.

EXAMPLE III been observed to accompany the use of a low molecular (a) A copolyarnide, viz., poly(hexamethy1ene adipamide/terephthalamide) 70/ 30 by weight with a relative viscosity of 42 (inherent viscosity of about 1.05) was made by melt polymerization of the salts of adipic and terephthalic acid with hexamethylene diamine. A copolyamide, poly(hexamethylene adipamide/epsilon caproamide) /40 by weight with a relative viscosity of 35 (inherent viscosity of about 0.95) was made from hexamethylene diammonium adipate and caprolactam using the technique of Brubaker US. Patent No. 2,285,009, issued June 2, 1942. The above polymers were spun as sheaths and cores respectively of composite filaments as in Example I. The yarn was drawn 239% (3.4 i.e., 3.4 times the length of the undrawn filament) over a pin at 80 C. and immediately thereafter over and in contact with a plate at 160 C. Monofilaments of the two separate polymers shrunk 8% and 25% in boiling water under 0 g.p.d. tension, respectively, after spinning and drawing under conditions similar to those of the preceding paragraph.

weight polymer as a low shrinking member of a composite filament.

It is desired to point out that although the improved thermal crimp stability corresponding to a crimp loss not exceeding 40% is preferred and readily obtained by the practice of the invention, the invention has substantial advantage even though the crimp loss be greater, e.g., 60%, as shown in Example I, above, since comparative data shows the great improvement in such crimped filaments made by the use of the invention as compared with those made without the use of this invention.

It was surprising that the core polymers containing aromatic groups were remarkably superior over the control with regard to the crimp developed. Furthermore, these aromatic group-containing polymers have a higher initial modulus (Mi) and a higher melt viscosity than polymers containing only aliphatic groups. A higher modulus is preferred for the low shrinking component of the crimpable filaments of this invention so as to gain the highest crimp elongation.

Table III (Example IV) Viscosity Crimped composite yarn properties Denier Percent Gore polymer type (drawn) Complete Radius of crimp Mn Relative Inherent Melt at yarn turns 1 curvature 1 elongation 1 275 denierper inch in inches from 0.0

number of crimping filaments tension Poly(p-Xylylene aselaminde) 300 60-17 72 016 310 Poly[p-bis(ethyl amino) benzene sebacamide] 3 300 15- 1 46 026 295 Poly (hexarnethylene terephthalarnide/adipamide) 3 35/65 eopolyrner 150 24 7 60 0.19 240 Poly(hexa.methylene adipamide)contrl 100 70-34 50 022 150 1 Measured on yarns erimped under 0 g.p.d. tension. 2 60C. water. 3 Formed by polymerization technique described in Uarothers U.S. Patent No. 2,252,554.

The composite filaments of this invention contain two 2,667,468. Polymers containing both carbonamide polymers which diifer in their shrinkage capacity. The higher shrinking component becomes the load-bearing member of the crimped yam and hence should be selected from polymers having excellent tensile recovery proper ties in order that the crirnped yarn can maintain its crimp against repeated deformations or elongations. A tensile recovery (dry) of at least 90% from a 5% elongation at room temperature is preferred. The load-bearing member preferably has a sufliciently high initial modulus, preferably at least 50 in order that the crimp will not be loose and weak.

Since it is the shrinking force of the higher shrinking or load-bearing component that determines the intensity of crimp, the higher shrinking or load-bearing component should, in the final, potentially crirnpable filaments, have a shrinkage of at least 2% greater (preferably as tested by shrinkage in boiling water under a tension of 0 g.p.d.) than that of the lower shrinking component. It is, moreover, preferred that the higher shrinking component of the final, potentially crimpable filament, have a shrinkage of at least 5% in boiling water under 6.1 g.p.d. restraining tension. The shrinkage characteristics of the loadbearing component can be readily determined by testing the shrinkage of a monofi lament composed of the polymer comprising said load-bearing component and prepared under conditions similar to those used in preparing the composite filament.

Because of their commercial availability, ease of processing and excellent properties, the condensation polymers and copolymers, e.g., polyamides, polysulfonamides and polyesters, and particularly those that can be readily melt spun are preferred for application as both components in this method. Suitable polymers can be found, for instance, among the fiber-forming polyamides and polyesters which are described in US. Patents Nos. 2,071,250, 2,071,253, 2,130.523, 2,130,948, 2,190,770, and 2,465,319. The preferred group of polyamides comprises such polymers as poly(hexamethylene adipamide), poly(hexamethylene sebacamide), poly(epsi=lon caproamide) and the copolymers thereof. Among the polyesters that may be mentioned, besides poly( ethylene terephthalate), as suitable for use as either or both components of the composite filaments of this invention, are the corresponding copolymers of ethylene terephthalate containing sebacic acid, adipic acid, isophthalic acid, as well as the polyesters containing recurring units derived from glycols with more than two carbons in the chain.

Fiber-forming polysulfonamides can be produced by reacting at an interface between two immiscible phases organic sulfonic acid halides, e.g., dichlorides, which form or are contained in one phase, with primary or secondary organic diamines which form or are contained in the other phase, whereby preferably one of the phases is dispersed in the other while the reaction takes place. Such a method is described, for instance, in U.S. Patent No.

groups and sulfonamide groups may be used.

The above-described interfacial polymerization methods may also be used for producing polyamides, when organic dicarboxylic acid halides are used instead of the sulfonic acid halides. Other groups of polymers useful as components in filaments of the present invention can be found among the polyurethanes or the polyureas which may be made either by conventional methods or by the above-described interfacial methods, as well as among the polyvinyl compounds, including such polymers as polyethylene, polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride, and similar polymers.

The polymer used as the lower shrinking member of the final, potentially crimpable composite filament should have as low a shrinkage as possible under the processing conditions used. The exact shrinkage value as required will depend upon the other component inasmuch as it is the difference in shrinkage that controls the crimp. A shrinkage in boiling water of no more than 3% under a tension of 0 g.p.d. is preferred for the lower shrinking member of the final, potentially crimpable filament; this is determined by measuring the shrinkage of a monocomponent filament composed of the polymer comprising the lower shrinking component and made under conditions similar to those used in preparing the composite potentially crimpable filament.

A preferred class of polymer for use as a lower shrinking member of a composite filament comprises those condensation polymers containing an aromatic group intralinear to the polymer chain. These include polyamides and polyesters made from such dibasic acids and diamines as: terephthalic acid, isophthalic acid, p-Xylylene diamine, p-bis(ethyl amino)benzene, p-phenylenediamine, 4,4-diamino diphenylmethane, benzenediacetic acid, 4,4'-diactodiphenylmethane, to name a few, and other monomers as desired. The physical properties such as melting point, solubility or melt viscosity of the homopolymer containing the preferred aromatic constituent may be modified as desired by copolymerization. The presence of as little as 20 mol percent of the aromatic monomer combined in the low shrinking polymer molecule is effective, but 25 to 75 mol percent is preferred. The core polymer is preferably crystalline to reduce shrinkage. Also, where a co-polymer is used, each monomer should be of such nature as not to interfere with the crystallization of the co-polymer; therefore, the copolymers are preferably made from monomers which are isomorphous with each other, i.e., they should crystallize in the same crystalline form, in order to maintain as low a shrinkage as possible.

The molecular weight of a polymer used for the production of synthetic fibers is usually a compromise between the various physical properties desired in the product, the ease of making the fiber including such processes as spinning, drawing, etc., and possibly the production of the polymer itself. Physical properties such as tenacity generally increase with increasing molecular weight. The

viscosity of a concentrated solution or melt of the polymer also increases with increasing molecular weight. However, too low a molecular weight polymer may be as diificult to spin because of its low viscosity as a very high molecular weight polymer may be, due to its very high viscosity so that an intermediate value of molecular weight may well be selected for use.

The invention may utilize as the load-bearing component a polymer having good fiber forming properties; generally speaking, the polymer for the load-bearing component is one which is acceptable for the commercial spinning and drawing of single component filaments from such polymer. The lowest molecular weight poly(hexamethylene adipamide) that is commercially spun and drawn at the present time as single component filaments is that which corresponds to a relative viscosity of 27 (inherent viscosity of about 0.87) but, for the production of first-class yarn, relative viscosity of 36 (inherent viscosity of about 0.98) and higher are now used. The commercially acceptable molecular weight levels of other polyamides will vary with the specific polymer but in general they will be of a magnitude comparable to the above.

Poly(ethylene terephthalate) of relative viscosity of 22 (intrinsic viscosity of about 0.53) is about the minimum for commercial spinning and drawing but relative viscosities of 27-33 (intrinsic viscosities of about 0.6 to 0.7) are currently used in commerce to avoid denier non-uniformities, spinning and drawing breaks, and low tenacities that are prevalent when using the minimum molecular weight.

It is preferred in the practice of this invention that the load-bearing component be a polymer which can be readily spun into mono-component filaments having a dry tenacity of at least 3 grams per denier, since this insures an acceptable tenacity in composite filaments containing such polymer.

For the low shrinking component of the filaments of this invention, polymers having relative viscosities of about 6 to 20 inclusive or (where the relative viscosity has not been determined) having molecular weights equal to those which have relative viscosities within said range, are preferred. Relative viscosities of 10-l5 inclusive for polyamides and 10-19 inclusive for polyesters, both ranges inclusive of copolyamides and copolyesters and other amide or ester copolymers, are preferred. These low viscosity values (and the corresponding molecular weights) are selected so that the molecular weight of the low shrinking component will be 75% or less of the lowest molecular weight of the same basic polymer acceptable for commercial spinning and drawing of single-component filaments; reference to the same basic polymer in this connection means that the polymer is made of the same polymer components in the same ratio in the polymer, the diiference in the polymers being in the degree of polyerization and, concomitantly, in molecular weight.

The exact viscosity values of other polymers which may be used as the low-shrinking component in the practice of this invention will depend on the minimum molecular weight of the same basic polymer acceptable for commercial production, which can readily be determined according to accepted commercial standards by those skilled in the art, but, as stated above these values are limited to polymers for the low-shrinking component which have molecular weights 75% or less of the said commercially acceptable minimum molecular Weight for the same basic polymer.

The lower values of molecular weight for polymers useful as the low-shrinkage components of this invention are chosen generally in accordance with the ability of the polymer to be spun with the sheath to produce a composite filament having the desired physical properties. The preferred polymers especially useful in this regard are those having an aromatic group in the polymer chain since they generally have a higher melt viscosity for a given inherent viscosity than do the non-aromatic polymers. Such higher melt viscosities afford better spinning of these polymers. By use of a sheath-core fiber construction, much lower molecular weight polymers can be spun as a core than with a fiber structure in which the components adhere in side-by-side relationship although the use of low molecular weight polymers as low-shrinking components in side-by-side filaments is comprehended by this invention.

The desired difference in shrinkage between the two components can be brought about by a number of processes. In some cases the extent of shrinkage will depend upon the drawing conditions. For example, poly(ethylene terephthalate), when simply cold-drawn, has a greater shrinkability than a cold-drawn polyamide, but when a hot plate treatment is included, following a hot pin drawing, the shrinkage tendencies are reversed and the polyester becomes the lower shrinking component. It is thought that this is due to a more rapid rate of crystallization and may arise from the difference between the apparent minimum crystallization temperature of the two polymers determined as described in US. Pat. No. 2,578,- 899. A difference in crystallization which may reverse or enhance the difference in shrinkage may also be brought about by the presence of a plasticizer in one component which will enable it to be crystallized more readily. The addition of certain substances also increases the rate of crystallization. For example, the presence of a small amount of finely divided BaSO incorporated into poly(ethylene terephthalate), doubles the rate of crystallization of the polymer. In addition, certain polar organic liquids which are latent solvents for the amorphous regions of one of the components, may be used to preferentially crystallize that component.

The composite filaments have been produced in the examples by the melt spinning technique. Other spinning methods, such as plasticized melt spinning, dry spinning, and wet spinning, can be employed successfully. In some instances, particularly when the melting behavior or the solubility of the components in a combination does not permit spinning the components by similar methods, a combination of dissimilar methods is indicated. Thus, for instance, one component, preferably the component forming the sheath can be spun as a solution in a highboiling solvent or as a plasticized melt, while the coreforming component is extruded as the molten polymer. In these instances, the media for solidifying the filaments are chosen in accordance with the components being spun, and the solvents or plasticizers may be wholly or partially removed subsequently, preferably by washing them out by the help of low-boiling solvents.

The composite filaments of this invention are substantially uncrimped after the drawing and subsequent heating treatment under tension but contain, however, a potential crimp. However, crimp due to retractive force, i.e., the crimp resulting from release of the force used in drawing the filaments, may, in some cases, be substantial. The crimp can be developed in the new filaments very readily by a suitable after-treatment. The filaments containing the potential crimp can be processed as any ordinary uncrimped continuous filaments or staple fibers to worsted or knitted goods. The crimp can then be imposed on the filaments at any time by a suitable relaxing or shrinkage treatment. This shrinkage treatment was performed in the foregoing examples by exposing the composite filament containing the potential crimp to hot water or steam. Which of these aftertreatments for bringing about the crimp are chosen depends mostly on the properties of the components forming the composite filaments and on the final properties which are desired in the crimped filaments. In general, the temperature applied in the crimping procedure should be higher than the apparent second-order transition temperatures (T of the polymers forming the composite filament in order to achieve the favorable results of the invention. A convenient method for measuring this sec ond-order temperature is shown in US. Patent No. 2,- 578,899. Since water acts as a plasticizer in many polymers, thus lowering the apparent second-order transition temperature (T this should also be considered in determining (T and in selecting the crimping temperature. Other factors influencing the optimum condition for crimping the composite filaments of this invention are the spinning, drawing, and length stabilizing conditions used and also other factors, for instance, whether the composite filament is to be processed as continuous filament or as staple, or as a woven or knitted textile fiber. Therefore, by varying the after-treating conditions for bringing about the crimp, also the properties and appearance of the crimped filaments can be varied to a great extent in any desired way.

In general, the composite filaments are drawn from about two times to about eight times their original lengths. Prior to drawing, the filaments are attenuated; that is, they are slendeiized by pulling the freshly extruded filaments away from the orifice at a rate faster than the extrusion rate. The drawing or orientation step is in addition to attenuation during spinning, but also has a slenderizing eifect. The extent of drawing will, of course, also depend somewhat upon the nature of the particular polymers used in the composite filament, upon the type of eccentric relationship between those polymers in the composite filament and spinning speed. Drawing will, in general, be maintained within the drawing limits of both filment components, so that not only the more drawable but also the less drawable component will not fracture and both components will be continuous throughout the filaments.

In the hot relaxing treatment of this invention used to develop the potential crimp, the medium may be any inert atmosphere capable of being heated to a temperature of about 100 C. Thus, the filaments may be heated free of tension or under very low tension, in air, nitrogen, hot or boiling water, carbon dioxide or any gaseous or liquid media inert to the polymers in the composite filaments although hot or boiling water is preferred. The temperature used is generally in the neighborhood of 100 C. but it may be lower or higher. For example, any temperature above about 50 C., but below the melting point of the lowest melting polymeric constituent in the composite fiber, may be used. Generally, a temperature in the range of 50 C. to 150 C. is quite satisfactory and effective.

The length of time that the composite filaments are subjected to the hot, relaxing treatment is not critical, because the crimp develops immediately and spontaneously. Thus, the time may be short, as, for example, a matter of seconds, although it may be desired in some cases to continue the length of treatment for a longer period of time such as thirty minutes, or even for several hours.

Although this invention has been illustrated with round filaments having an oblate circular core completely and eccentrically surrounded by a sheath, the invention is not limited thereto. Any filament structure which affords an eccentric arrangement of the two components can be used, as for example, a side-by-side structure as shown in FIGURE 5, or an eccentrically arranged circular core as shown in FIGURE 6. The cross-section of the composite filaments is not limited to circular shape but can be crennulated, dog-bone, or cruciform shape, etc. Preferably a sheath-core structure is used since the low molecular weight component may be diflicult or impossible to spin at commercial levels unless protected by :a shath of more viscous materials.

It is desired to point out that the shape of the core as well as that of the sheath as they appear in the undrawn filament, persist in the composite filament after l4 drawing in spite of diminution in the cross-section of the drawn filament.

The characteristics of these new crimped filaments make them especially useful for many textile applications where the uncrimped filaments may be knitted or woven into articles before crimping and exposure to subsequent high temperature processing that has previously caused a high loss of crimp as, for example, in elastic hosiery or carpets. The crimped filaments, either as continuous filaments or as staple fiber, can be used to fabricate bulky fabrics which are quite stable to hot condi tions.

While the invention has been particularly described with respect to two-component filaments, it will be understood that it applies in like fashion to filaments having 3 or more components provided that two of the components have the characteristics, e.g., shrinking differential, described herein with respect to components of a two-component filament.

The description contained herein is intended to be illustrative rather than limitative. Any variation or departure therefrom which conforms to the spirit of the invention is also intended to be included within the claims.

I claim:

1. A composite textile filament having at least two components in eccentric relationship across the filament, one component being a synthetic linear fiber-forming polymer selected from the group consisting of polyesters and polyamides and as another component eccentric to and continuous with said first component, a synthetic linear polymer selected from the group consisting of polyesters and polyamides having a molecular weight not exceeding 75% of its minimum fiber-forming molecular weight, said first component having a shrinkability of at least 2% greater than said second component and said composite filament developing a pronounced, highly heat stable crimp when shrunk from the straight state.

2. The composite filament of claim 1 wherein said second component has a relative viscosity of 6-20.

3. The composite filament of claim 1 wherein said second component is a polyester having a relative viscosity of 10-19.

4. The composite filament of claim 1 wherein said second component is a polyamide having a relative viscosity of 10-15.

5. The composite filament of claim 1 wherein the second component contains aromatic rings in the poly mer chain and has a relative viscosity of 6-20.

6. The composite filament of claim 1 wherein said second component is a polyester containing aromatic rings in the polymer chain and has a relative viscosity of 10-15.

7. The composite filament of claim 1 wherein said second component is a polyamide containing aromatic rings in the polymer chain and has a relative viscosity of 10-15.

8. The composite filament of claim 1 wherein both said first and second components are condensation polymers.

9. A composite textile filament having at least two components in eccentric relationship across the filament, one component being a synthetic linear fiber-forming polymer selected from the group consisting of polyesters and polyamides and as another component eccentric to and continuous with said first component, a synthetic linear polymer selected from the group consisting of polyesters and polyamides having a molecular weight below the minimum fiber-forming molecular weight, said first component having a shrinkability of at least 2% greater than said second component and said composite filament developing a pronounced, highly heat-stable crimp when shrunk from the straight state.

10. The composite filament of claim 9 wherein the polymers are condensation polymers.

11. The filament of claim 9 having a high degree of crimp.

12. The filament of claim 9 in the straight, potentially crimpable state.

13. The filament of claim 9 in which the filament has one component as a core and the other component as a sheath.

14. The filament of claim 9 in which the components are in side-by-side relationship.

15. A crimped composite textile filament having at least two components in eccentric relationship across the filament, one component being a synthetic linear fiber-forming polymer selected from the group consisting of polyesters and polyamides, and as another component eccentric to and continuous with said first component, a synthetic linear polymer selected from the group consisting of polyesters and polyamides having a molecular weight not exceeding 75% of its minimum fiber-forming molecular weight, the latter component being located on the outer portion of the helically crimped filament While the first component is located on the inner portion of the 16 helically crirnped filament, said first component having a shrinkability of at least 2% greater than said latter component.

References Cited in the file of this patent UNITED STATES PATENTS 2,428,046 Sisson et a1 Sept. 30, 1947 2,439,814 Sisson Apr. 20, 1948 2,612,679 Ladisch Oct. 7, 1952 2,614,288 Chavannes Oct. 21, 1952 2,674,025 Ladisch Apr. 6, 1954 2,687,673 Boone Aug. 31, 1954 2,716,049 Latour Aug. 23, 1955 2,737,436 Boeuf Mar. 6, 1956 FOREIGN PATENTS 514,638 Great Britain Nov. 14, 1939 744,112 Germany Jan. 10, 1944 760,179 Great Britain Oct. 31, 1956 1,124,921 France July 9, 1956 

1. COMPOSITE TEXTILE FILAMENT HAVING AT LEAST TWO COMPONENTS IN ECCENTRIC RELATIONSHIP ACROSS THE FILAMENT, ONE COMPONENT HEING A SYNTHETIC LINEAR FIBER-FORMING POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYESTERS AND POLYAMIDES AND AS ANOTHER COMPONENT ECCENTRIC TO AND CONTINUOUS WITH SAID FIRST COMPONENT, A SYNTHETIC LINEAR POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYESTERS AND POLYAMIDES HAVING A MOLECULAR WEIGHT NOT EXCEEDING 75% OF ITS MINIMUM FIBER-FORMING MOLECULAR WEIGHT, SAID FIRST COMPONENT HAVING A SHRINKABILITY OF AT LEAST 2% GREATER THAN SAID SECOND COMPONENT AND SAID COMPOSITE FILAMENT DEVELOPING A PRONOUNCED, HIGHLY HEATSTABLE CRIMP WHEN SHRUNK FROM THE STRAIGHT STATE. 